INDIANAPOLIS (AP) — Environmental activists who've spent weeks trying to decipher a proposed air permit for BP's planned Whiting refinery expansion said Tuesday they still have many unanswered questions about how the permit would affect northwest Indiana's air quality.

Monday was the last day of a public comment period on the permit, which was released Feb. 5 with a document that details BP's planned changes as part of a $3.8 billion refinery expansion.

Environmentalists had wanted more time to review the two documents because they're highly technical and each runs more than 1,300 pages, said Kim Ferraro, an attorney for the Valparaiso-based Legal Environmental Aid Foundation.

She said the public comment period for the permit, from Feb. 11 to Monday, was too short. That could hamstring activists if they later find something in the permit they believe violates the Clean Air Act and want to ask a judge to intervene to block the permit, Ferraro said.

"If we don't raise questions during the comment period we can't raise them on judicial review and we haven't had time to look at it to know what the problems are," she said.

BP's planned Whiting refinery expansion would turn the 1,400-acre complex about 20 miles southeast of Chicago into a hub for processing heavy Canadian crude oil.

A 200-page technical and legal commentary letter prepared by the Chicago-based Natural Resources Defense Council and submitted to IDEM points to what it and other groups call numerous deficiencies with the permit.

Tom Anderson, executive director of the Save the Dunes Council, said high among those concerns for his Michigan City-based group are three large flares that will be added to the refinery.

Oil refineries use flares — tall chimney-like structures — to burn off waste substances. But the Natural Resources Defense Council and Anderson said those flares' emissions are not included in the overall air emissions expected from the expanded refinery.

"Our question is why haven't they been included? They obviously need to be included to have a total picture of the impact of this project," Anderson said.

Rob Elstro, a spokesman for the Indiana Department of Environmental Management, said the agency believes its analysis of the refinery's emissions takes into account the flares' emissions. However, he said IDEM is checking to make sure that's the case.

"We're taking another look at it because we've received comments about it, but we think we've already addressed those emissions in the permit," he said.

During a March 14 public meeting and hearing on the permit, IDEM officials said they expected to approve the permit within about six weeks, Elstro said.

If that happens, the permit would be approved before June 1, when air emission credits that BP earned for improvements it made to the refinery in 2003 will expire.

BP hopes to use those credits and other credits it received from upgrades made after 2003 to offset some of the emissions that the expanded refinery will produce.

With those credits factored in, BP has said the refinery's net emissions would actually decrease when the expansion goes online in 2011, even though particulate matter and sulfur dioxide emissions would increase.

Ferraro said that if IDEM had approved activists' request for another month of so to review the permit, that would have put BP of risk of not getting the permit approved before June 1, when some of the credits expire.

She contends that BP is using the credits to avoid making even deeper cuts that could reduce the refinery's emissions further and help improve northwestern Indiana's air quality.

Ferraro said IDEM has not changed its approach to the permitting process despite last summer's uproar over a water discharge permit that BP obtained for the project.

Environmentalists said that permit, approved last June, would add to pollution in Lake Michigan, which Chicago and other cities in Illinois and Indiana use for their drinking water.

In August, after weeks of criticism, BP said it would find a way to comply with the lower ammonia and suspended solids discharges set in its earlier permit or cancel the expansion.